The present invention relates to mobile communications, and more particularly, to the efficient allocation and use of resources in a mobile communications network.
Current mobile telecommunications networks are typically designed to connect and function with Public Switched Telephone Networks (PSTNs) and Integrated Services Digital Networks (ISDNs). Both of these networks are circuit-switched networks and handle relatively narrow bandwidth traffic. However, packet-switched networks, such as the Internet, handle much wider bandwidth traffic. While wireline communication terminals, e.g., personal computers, are capable of utilizing the wider packet-switched network bandwidth, wireless mobile radio terminals are at a considerable disadvantage because of the relatively limited bandwidth of the radio/air interface that separates the mobile terminals from packet-switched networks. In the second generation Global System for Mobile communications (GSM) mobile communications system, a General Packet Radio Service (GPRS) was introduced to handle xe2x80x9cburstyxe2x80x9d traffic such as the infrequent transmission of e-mail messages, Internet information, and other data. Because GPRS is a packet-switching service, it only requires radio channel resources when data is actually being sent as compared to typically less efficient circuit-switched services that are reserved for a mobile user regardless of whether data is actually being sent. The GPRS packet-switched service enables the radio frequency spectrum to be more efficiently allocated across voice and data calls and allows channels to be shared between several users simultaneously.
Even though GSM provides both circuit-switched and packet-switched services to mobile users, GSM and other second generation mobile communication systems still suffer from narrow radio bandwidth. Radio access is needed that provides very high data rates and supports enhanced bearer services not realistically attainable with existing generation mobile communication systems. A third generation of mobile systems based on Wideband Code Division Multiple Access (W-CDMA) radio access is being introduced. Unlike narrow band access methods such as Frequency Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA), and to some extent xe2x80x9cregularxe2x80x9d CDMA, W-CDMA currently supports 5 MHz to 15 MHz of bandwidth, and in the future, promises an even greater bandwidth. In addition to wide bandwidth, W-CDMA also improves the quality of service by providing robust operation in fading environments and transparent handovers between base stations (soft handover) and between base station sectors (softer handover). Multipath fading is used to advantage to enhance received signal quality, i.e., using a RAKE receiver and improved signal processing techniques, contrasted with narrow band mobile communications systems where fading substantially degrades signal quality.
Another limitation with the current GSM system is that it offers basically two categories of services: circuit-switched services through one particular type of network service node, such as a Mobile Switching Center (MSC) node, and packet-switched services offered through another type of network service node, such as a GPRS node. There is one set of channels for circuit-switched services and another different set of channels for packet-switched channels. There is not much flexibility to mix and match particular services to meet often changing needs of mobile subscribers. In contrast, the W-CDMA system provides a wide variety of services and enables flexible allocation of resources and delivery of requested services. Indeed, a single set of channels is used to support both circuit-switched and packet-switched services. Current needs for a particular service are analyzed, and then existing communication resources are flexibly and dynamically assigned taking into account current demands in the system for communications resources.
An example third generation, W-CDMA system, sometimes referred to as Universal Mobile Telecommunications System (UMTS) is shown in FIG. 1. The UMTS 10 includes a representative, connection-oriented, external core network, shown as a cloud 12, may be for example the PSTN or ISDN networks. A representative, connectionless-, external core network, shown as a cloud 14, may be for example the Internet. Both core networks are coupled to a corresponding service node 16. Core network 12 is connected to a connection-oriented service node shown as a mobile switching center node 18 which provides circuit-switched services. In the existing GSM model, the mobile switching center 18 is connected over an interface A to a Base Station System (BSS) 22 which in turn is connected to a radio base station 23 over an interface Abis. The Internet connectionless-network 14 is connected to a GPRS node 20 tailored to provide to packet-switched services. Each of the core network services 18 and 20 connects to a UMTS Terrestrial Radio Access Network (UTRAN) 24 over a Radio Access Network (RAN) interface. The UTRAN 24 includes plural Radio Network Controllers (RNCs) 26. Each RNC 26 is connected to a plurality of base stations (BS) 28 and to any other RNCs in the UTRAN 24. Radio communications between the base stations 28 and mobile stations (MSs) 30 are by way of a radio/air interface.
In the preferred example embodiment, radio access is based on WCDMA with individual radio channels being allocated using WCDMA spreading codes. The UTRAN 24 provides services to and from mobile stations over the radio interface for the external core networks 12 and 14 (and ultimately to external, core network end users) without then having to request specific radio resources necessary to provide those services. The UTRAN 24 essentially hides those details from the service nodes, external networks, and users. Instead, a xe2x80x9clogicalxe2x80x9d radio access xe2x80x9cbearerxe2x80x9d is simply requested from UTRAN 24 by a service node 16. A radio access bearer corresponds to the UTRAN service actually carrying user data through the UTRAN and over the radio interface. The term xe2x80x9cconnectionxe2x80x9d corresponds to the collection of all radio access bearers plus the control signaling associated with one particular mobile station.
It is the task of the UTRAN 24 to map the mobile connection onto physical transport channels in a flexible, efficient, and optimal manner. Thus, each service node simply requests one or more radio access bearers with a mobile station where each bearer may have an associated quality of service. Quality of service may include for example a desired bit rate, an amount of delay before information is transferred, a minimum bit error rate, etc. The UTRAN 24, in response to radio access request to support a connection, assigns transmission resources (e.g., an ATM transport connection) through the UTRAN 24 and a radio channel (e.g., a spreading code) over the radio interface.
In mapping a radio access connection onto one or more specific radio channels, the UTRAN 24 flexibly balances and optimizes a number of parameters including quality of service, range (distance between mobile station and base station), traffic load-capacity, and mobile station transmission power. One of two different types of radio channels may be selected by the RNC 26 to support a mobile connection: a dedicated or a common channel. The two radio channel types differ by the degree of radio resource reservation per channel. For a dedicated radio channel, resources in terms of spreading code(s) and power/interference are allocated to this particular mobile station. A common radio channel is a resource (spreading code) that is shared dynamically between multiple mobile stations. Based on the requested quality of service and the current traffic conditions, the RNC 26 may select the type of radio channel to carry the information associated with the radio access bearer service request.
As an example, if high quality of service with low delay guarantee is required, the RNC 26 may map the connection onto a dedicated channel. Moreover, a dedicated channel supports diversity handoff including soft and softer handoff as well as fast power control. These features improve the quality of communications in CDMA communications, and also provide for efficient transfer of a continuous stream of data. For delay tolerant, infrequent, or small size packet data, the RNC 26 may map a connection onto a common (shared) packet channel. Although a dedicated channel may use radio resources inefficiently because the channel remains dedicated even when no information is being transmit, a common-type channel offers connectionless transport that can be scheduled providing a more efficient use of the radio channel resources.
Using the best type of channel may be important even during the life of a single radio access bearer. In fact, switching of the type of channel supporting an ongoing radio access bearer may be initiated because:
channel conditions have changed
a radio access bearer has been added to or removed from the connection
the amount of packet data to be transmitted has changed significantly.
For example, a connection exists between one mobile station and the network with one radio access bearer established for background packet data. The connection employs a common channel. If the user initiates a speech call, then an additional radio access bearer for the speech is established. The connection then includes two radio access bearers. Since the speech requires a radio access bearer with low delay and resource reservation requiring a dedicated channel, the connection will be switched to a dedicated channel. As another example, a dedicated channel may be set up to support a connection in which a large amount of data is initially transmit over a radio access bearer. After that transmission, small amounts or bursts of data may be transmitted more efficiently on a common packet-type of channel resulting in a switch from a dedicated channel to a common channel to support the connection. Moreover, it may be efficient or even necessary to switch the connection back to a dedicated channel if the amount of data or traffic conditions or other factors demand.
However, channel-type switching to maximize the use of radio resources to accommodate a requested service, adapt to current traffic conditions, etc. incurs a xe2x80x9cchannel switching cost.xe2x80x9d Setting up and taking down a channel requires a certain amount of data processing resources and a specific amount of delay time to perform. For example, before switching from a common-type channel to a dedicated channel, the xe2x80x9cservingxe2x80x9d RNC for a connection (and possibly other RNCs supporting the connection), must first reserve transmission resources between the serving RNC (and any other supporting RNCs) and the base station as well as request the base station to set up both hardware and software resources for this particular connection. After switching from a dedicated to a common-type channel, the serving RNC orders the base station to release all base station resources related to the dedicated connection and also releases dedicated channel transmission resources for this connection in the UTRAN. Each channel-type switch may incur set-up/release costs for multiple, parallel transmission bearers if the connection requires support of multiple services and/or multiple transport channels. When using a dedicated channel, there is normally a transport channel for each radio access bearer. Each transport channel uses its own UTRAN transmission resource, e.g., an AAL2/ATM connection, between the RNC and the base station when using a dedicated channel. Switching from a common type radio channel to a dedicated radio channel may also require other procedures including, for example, reserving a diversity handover resource in the RNC. Switching in the other direction from a dedicated channel to a common channel is not as costly because the common channel was already established when the system was configured and typically remains established as long as the system is operational.
It would be desirable to reduce channel-type switching costs if possible without sacrificing the flexibility and efficiency that channel-type switching offers.
A channel switching cost is also incurred during handover operations. While handover operations in general provide mobility and other advantages, e.g., diversity handover improves the quality of communication, there is a cost in adding and releasing the mobile connection in each cell involved in a mobile handover operation. The cost of a new cell to support the connection includes, for example, network signaling to reserve resources in the base station, establishing a transmission resource between the network and the base station, signaling between the mobile station and the base station to add a particular cell, and performing these operations in reverse sequence when a cell is no longer supporting a connection. In soft handover procedures, before adding a cell to a set of cells currently supporting a connection, a serving RNC must first request the base station (possibly by way of another supporting RNC) to set up both hardware and software resources for this particular connection as well as establish transmission resources between the serving RNC and the base station possibly by way of a supporting RNC. If the mobile is ordered to release a cell from the current set, the serving RNC (and possibly other supporting RNCs) releases the transmission resources between the RNC(s) and the base station as well as the resources in the base station. In cases where several parallel services require multiple transport channels, each addition/drop of a cell incurs the set-up/release of several parallel transmission resources.
The adding and dropping of cells in handover uses precious radio resources and is often triggered by rapid changes in the radio environment. Therefore, the faster cells can be added and dropped, the better the handover operation adapts to the current radio environment. It is not uncommon for a mobile station to be located at the border between two or more cells, and in that situation, cells may be added and dropped several times during the life of a connection in order to optimize radio performance, e.g., due to fast multipath fading, etc. If the set-up and release procedures between the RNC(s) and base station(s) just described are employed for each addition/release of a cell, the rate at which soft handover is performed is limited both by the data processing load incurred and by the delay in executing each cell addition or release.
It is an object of the invention to provide flexible and efficient allocation of resources in a mobile communications system.
It is an object of the present invention to minimize channel switching costs including delay such as those associated with channel-type switching and handover operations.
It is an object of the present invention to provide different levels of adaptiveness to various situations, including the radio environment, user data traffic, etc. for handling radio resources and radio network resources that support a particular connection. For example, it may be desirable in some situations to provide rapid allocation of radio resources to optimize radio interface performance in response to changing conditions while providing less rapid response within the radio access network.
The present invention provides a solution to the problems described above and meets these and other objects by providing efficient channel switching procedures in a mobile communications system. In general, a first channel is established to support a connection through a radio access network to a mobile station. Subsequently, if the first channel is no longer used to support that connection, a portion of that first channel is nevertheless maintained for a period of time. That way, if the first channel is again needed to support the connection to the mobile station, the maintained portion of the first channel is simply reactivated thereby avoiding channel switching costs associated with channel set-up and release operations. The portion of the first channel that is maintained may be associated, for example, with resources in the radio access network. Another portion of the first channel, corresponding to a radio channel resource supporting the connection between the radio access network and the mobile station, may be released after the first channel is no longer being used to support the connection in order to make that radio channel resource available for other mobile connections.
The radio channel resource may be viewed as a single resource or as plural resources. In the latter situation, plural radio channel resources may include for example (1) spreading codes or other physical radio channels and (2) power resources. It may be preferable in some situations to only release one of the plural radio channel resources. For example, a power resource is released simply by stopping transmission using an assigned spreading code. However, the spreading code itself is not released to be used in other connections. This provides particularly fast release and re-establishment procedures because spreading code de-allocation and re-allocation signaling with the RNC is avoided. A simple xe2x80x9ctransmission ONxe2x80x9d or xe2x80x9ctransmission OFFxe2x80x9d signal may be sent xe2x80x9cin-bandxe2x80x9d over the established dedicated transport channel and radio channel. In addition, the interference level is reduced which is very desirable in spread spectrum based communications systems.
The first channel may correspond in one example to a dedicated type of channel that is reserved just for the connection with the mobile station. The connection is switched to a second type of channel corresponding to a common channel that is not reserved for a particular mobile station, i.e., it is shared by plural mobile stations. The invention allows the connection to be quickly and efficiently switched back to the dedicated channel.
In another example, the first channel is one of plural channels established between the mobile station and the radio access network in accordance with a handover operation. During the handover operation, the connection is handed over from a first radio access network cell where the first channel is established to a second radio access network cell where a second channel is established to support a connection from the radio access network to the mobile station.
The portion of the channel that is maintained for a period of time after the channel is no longer being used to support the connection may include plural subportions. Any of the subportions may be maintained or released as desired when that channel is no longer needed. For example, a first subportion may be associated with resources within a radio network control node such as the RNC in FIG. 1. A second subportion may correspond to transmission resources on the link between the radio network control node and a base station. A third subportion may be associated with resources within the one base station. A fourth subportion may correspond to one of plural radio resources.
By maintaining one or more portions of the first channel, the signaling and processor costs as well as the delay associated with re-establishing that first channel are reduced. In addition, the radio resource(s) used to complete the channel between the base station and the mobile station can be quickly and selectively released. Quick release and re-establishment of the channel makes quick radio resource reallocations possible, thereby ensuring that the limited radio resources are optimally utilized.